This invention relates to a lever operated friction clutch and more particularly to a hydraulic unit for operating such a clutch.
Hydraulically operated friction clutches are well known and have found wide acceptance in the market place since they eliminate the need for external linkage such as levers, links and springs required to effect the operation in mechanically operated clutches. Not only do the hydraulic units require less space than the mechanical units but they also permit a vehicle operator to make use of a hydraulic system which is already available on existing highwayvehicles.
Hydraulic units are provided which operate to effect both the engaging and disengaging operation of the clutch and also to control these operations independent of each other. In the latter case, the opposite operation is achieved by some form of resilient means. For example, if the hydraulic unit is responsive to apply a pressure to effect clutch engagement then the resilient means is made to respond to disengage the clutch.
For a number of reasons, it has been found that the most satisfactory arrangement is one in which the hydraulic unit performs only one of the operations and the resilient means the other. One major reason for this is that less hardware is required. If the hydraulic unit is used for both operations, additional circuitry and controls are required. Not only does this increase the cost of the unit but it further makes such an arrangement undesirable since it requires much more space. Further, there is a definite advantage in having a unit in which the normally engaged position is achieved by the hydraulic unit and the resilient means is responsive to disengage the clutch. This type of construction provides an operator with a failure mode which is more desirable, i.e., if the hydraulic system malfunctions, the clutch will assume a disengaged position since the resilient means takes over in the absence of hydraulic pressure.
While hydraulic units designed to provide a pressure to accomplish one of the operations and resilient means for the other are generally satisfactory, they do have certain shortcomings. One of the drawbacks in known hydraulic units of this type is that they are constructed to fit specific applications and cannot be substituted for or in the space normally occupied by the mechanical operating parts in existing clutch applications. Also, many of these units are not easily serviceable because of the location of the unit and also the complicated or oversized construction of the operating parts.
The present invention is intended to solve the above problems by providing a hydraulic unit which is compact and readily adaptable for use in conventional clutch applications.